Thermosetting powder-type coating compositions

ABSTRACT

A method for making glycidyl ether-functional (meth)acrylate copolymers includes the step of reacting a hydroxyalkyl-functional (meth)acrylate copolymer with an epihalohydrin in the presence of a suitable catalyst. The reactants may be reacted by an addition reaction catalyzed with a Lewis acid catalyst, followed by dehydrohalogenation with aqueous alkali solution. Alternatively, the reactants may be reacted in a phase transfer reaction employing quaternary ammonium or quaternary phosphonium phase transfer catalysts.

This is a division, of application Ser. No. 08/623,856, filed Mar. 26,1996 now U.S. Pat. No. 5,844,048.

FIELD OF THE INVENTION

This invention concerns powder coating compositions that are capable ofbeing hardened or cured by means of heat, on the basis of acrylatecopolymers containing epoxide groups, together with suitable curingagents and/or pigments and/or fillers and/or additives, whereby theepoxide-containing acrylate copolymer is capable of being prepared by apolymer-like reaction of hydroxyl-functional acrylate copolymers withepihaloalkanes.

BACKGROUND OF THE INVENTION

Acrylate copolymers containing epoxide groups and their use as bindingagents in powder coatings are already known: See, for example, UnitedStates patents: U.S. Pat. No. 3,781,379, U.S. Pat. No. 4,042,645 andU.S. Pat. No. 4,346,144(incorporated herein by reference). As far as thehardeners are concerned, use can be made in this connection of polybasicacids or, preferably, dibasic acids, and their anhydrides or substancesthat form a dibasic acid under the conditions that prevail duringhardening. In principle, use can also be made of othercarboxy-functional compounds as hardeners such as, for example,amorphous and/or semi-crystalline polyester resins and/or acrylateresins with free carboxy groups.

The copolymers that are described in the aforementioned patents allcontain glycidyl acrylate, or, as the case may be glycidyl methacrylate.The rest of the copolymer consists of other unsaturated monomers, i.e.,one is dealing here with acrylate copolymers that contain glycidylesters. The preparation of monomeric glycidyl (meth)acrylate is notsimple from a technical standpoint since glycidyl (meth)acrylate readilypolymerizes, and the isolation of the pure monomer is veryproblematical. In addition to the short storage stability of glycidyl(meth)acrylate, its high toxicity also presents problems duringprocessing. Thus the preparation of acrylate polymers that containglycidyl esters via the copolymerization of glycidyl (meth)acrylate isproblematical and not recommended. A further disadvantage of thisprocess is that water cannot be used as the-reaction medium.

U.S. Pat. No. 3,294,769 (incorporated herein by reference) describes, ingeneral, a process for the preparation of acrylate polymers that containglycidyl ester groups via the reaction of carboxy-functional acrylatepolymers with epichlorohydrin.

The saponification of methyl methacrylate polymers and their subsequentreaction with epichlorohydrin has been investigated by Sandner et al.(see, Angew. Makromol. Chem., 181: 171-182(1990) and Makromol. Chem.,192: 762-777(1991)).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide thermosetting powdercoating compositions comprising acrylate copolymers that contain epoxidegroups, whereby the coating compositions contain special acrylatecopolymers as binding agents. These compositions avoid theaforementioned disadvantages of the prior art.

This and other objects are accomplished by the coating compositions, theprocesses for their preparation, the methods of using such coatingcompositions, the processes for preparing powder coatings as well as thepowder coatings themselves, which are described in the following textand in the claims.

DETAILED DESCRIPTION OF THE INVENTION

Surprisingly, it has been found that acrylate copolymers containingglycidyl ether groups can be prepared in a polymer-like reaction byreacting hydroxyl-functional acrylate copolymers with epihaloalkanes.

The subject of the invention is therefore thermosetting powder coatingcompositions comprising:

(A) a glycidyl ether-containing acrylate copolymer;

(B) an aliphatic and/or cycloaliphatic polybasic acid and/or itsanhydride and/or a polyol-modified anhydride of a polybasic acid and/oramorphous or semi-crystalline carboxy-functional copolyester resinsand/or carboxy-functional acrylate resins;

(C) and, optionally, fillers and/or pigments and/or additives; wherebythe glycidyl ether-containing acrylate copolymer has a molecular weight(Mw) of 1,000 to 30,000 and a glass transition temperature of 20° C. to120° C. and is obtainable by, in a first step, preparing a copolymer (D)that contains hydroxyl groups, which copolymer (D) is then transformed,in further steps, into an epoxide-containing acrylate copolymer (A) viareaction with epihaloalkanes. The copolymer (D) is obtainable, inparticular, via the copolymerization of a monomer mixture comprising thefollowing components:

(a) 0 to 70 parts by weight of methyl (meth)acrylate;

(b) 0 to 60 parts by weight of (cyclo)alkyl esters of acrylic acidand/or methacrylic acid with 2 to 18 carbon atoms in the alkyl or, asthe case may be, in the cycloalkyl residue;

(c) 0 to 90 parts by weight of vinyl aromatic compounds and

(d) 1 to 95 parts by weight of hydroxyalkyl esters of acrylic acidand/or methacrylic acid, whereby the sum of the parts by weight ofcomponents (a) through (d) results in 100.

Hydroxyl-functional acrylate copolymers are preferred with an OH numberof 10 to 400 or, preferably, from 20 to 300 mg KOH/g!.

The monomers (b) are preferably (cyclo)alkyl esters of acrylic acid ormethacrylic acid with 2 to 18 carbon atoms in the (cyclo)alkyl residue.Examples of especially suitable monomers (b) are: ethyl (meth)acrylate,n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl(meth)-acrylate, isobutyl (meth)acrylate, tert.-butyl (meth)acrylate,2-ethylhexyl (meth)acrylate, cyclohexyl methacrylate, neopentylmethacrylate, isobornyl methacrylate, 3,3,5-trimethylcyclohexylmethacrylate and stearyl methacrylate. Mixtures of the aforementionedmonomers can also be used.

The monomers (c) include, for example, styrene, vinyltoluene andα-ethylstyrene.

Suitable monomers (d) are the hydroxyalkyl esters of acrylic acid and/ormethacrylic acid with 2 to 6 carbon atoms, preferably 2 to 4 carbonatoms, in the hydroxyl residue such as, for example, 2-hydroxyethyl(meth)acrylate and hydroxypropyl (meth)acrylate (i.e., the mixture ofisomers that is formed during the addition of propylene oxide to(meth)acrylic acid), 4-hydroxy-n-butyl acrylate or also additionproducts of ε-caprolactone to the aforementioned simple hydroxyalkylesters. Thus the term "hydroxyalkyl ester" will also encompass residueshaving ester groups which are produced by the addition of ε-caprolactoneto simple hydroxyalkyl esters with 2 to 6 carbon atoms in the hydroxylresidue. In addition, the reaction products of glycidyl (meth)acrylatewith saturated monocarboxylic acids and the reaction products of(meth)acrylic acid with saturated monoepoxides, that can also carry OHgroups, can be regarded as "hydroxyalkyl esters" of (meth)acrylic acidand are therefore also suitable as monomers (d).

The preparation of the copolymers can be accomplished bycopolymerization of the monomers (a) to (d) already described byconventional radical-type polymerization processes such as, for example,solution polymerization, emulsion polymerization, pearl polymerizationor bulk polymerization. In this connection, the monomers arecopolymerized at temperatures of 60° C. to 160° C., preferably 80° C. to150° C., in the presence of a free radical initiator together, ifnecessary, with molecular weight regulators.

The preparation of the hydroxyl-functional acrylate copolymers may becarried out in inert solvents. Suitable solvents are, for example,aromatic compounds such as benzene, toluene and xylene; esters, such asethyl acetate, butyl acetate, hexyl acetate, heptyl acetate,methylglycol acetate, ethylglycol acetate and methoxypropyl acetate;ethers, such as tetrahydrofuran, dioxane, diethylene glycol dimethylether; ketones, such as acetone, methyl ethyl ketone, methyl isobutylketone; methyl n-amyl ketone, methyl isoamyl ketone or any desiredmixtures of such solvents.

The preparation of the copolymers can take place either continuously ordiscontinuously. Usually, the monomer mixture and the initiator areevenly and continuously metered into a polymerization reactor and thecorresponding quantity of polymer is continuously drained off at thesame time. Chemically virtually uniform copolymers also canadvantageously be prepared in this way. Chemically virtually uniformcopolymers also can be prepared by allowing the reaction mixture to run,at a constant rate, in a stirred vessel without draining off thepolymerizate.

A portion of the monomers can be introduced into the vessel, for examplein solvents of the type described above, and then the rest of themonomers and the auxiliary agents can be introduced, separately ortogether, into this mixture at the reaction temperature.

In general, polymerization takes place under atmospheric pressure;however, it can also be carried out at pressures up to 25 bars. Theinitiators are used in quantities of 0.05 to 15% by weight based on thetotal quantity of the monomers.

Suitable initiators include common radical-type initiators such as, forexample, aliphatic azo compounds such as azodiisobutyro-nitrile,azo-bis-2-methylvaleronitrile, 1,1'-azo-bis-1-cyclohexanecarbonitrileand the alkyl esters of 2,2'-azo-bis-isobutyric acid; symmetrical diacylperoxides such as, for example, acetyl peroxide, propionyl peroxide orbutyryl peroxide or benzoyl peroxides that have been substituted withbromine groups, nitro groups, methyl groups or methoxy groups, andlauryl peroxide; symmetrical peroxy dicarbonates, e.g., tert.-butylperbenzoate; hydroperoxides such as, for example, tert.-butylhydroperoxide, cumene hydroperoxide; dialkyl peroxides such as dicumylperoxide, tert.-butylcumyl peroxide or di-tert.-butyl peroxide.

In order to regulate the molecular weight of the copolymers, use can bemade of conventional regulators during the preparation. One maydesignate, by way of example, mercaptopropionic acid,tert.-dodecylmercaptan, n-dodecylmercaptan or diisopropyl-xanthogendisulfide. The regulators can be added in quantities of 0.1 to 10% byweight based on the total quantity of the monomers.

The solution of the copolymers generated during copolymerization canthen be fed, without further processing, into an evaporation process or,as the case may be, a gas removal process, in which the solvent isremoved, for example, in an evaporator extruder or spray dryer atapproximately 120° C. to 160° C. under a vacuum of 100 to 300 mbars, andthe copolymers that are to be used in accordance with the invention arerecovered.

The reaction of the hydroxyl-functional copolymers (D) withepihaloalkanes to give the epoxide-containing acrylate copolymers (A)according to the invention takes place in the manner that is usual forthe preparation of glycidyl ethers.

The glycidyl ethers of the hydroxyl-functional acrylate copolymers areobtained by reacting the hydroxyl-functional acrylate copolymer withepihaloalkanes. As a rule, this reaction takes place in a two-stepprocess. In the first step, the epihaloalkane is added to the hydroxylgroup of the acrylate copolymer, whereby a polyhalohydrin ether isformed. This reaction is catalyzed by Lewis acids such as, for example,boron trifluoride, tin tetrachloride, etc. Inert solvents such as, forexample, benzene, toluene, chloroform, etc. are suitable as the solvent,or the reaction can take place in an excess of the epihaloalkane, whichsimultaneously serves as a solvent.

In the subsequent two steps, the glycidyl ether acrylate copolymer isformed by means of a dehydrohalogenation reaction in an inert solvent,for example, using an aqueous caustic alkali solution, for exampleaqueous sodium hydroxide solution.

Together with the water from the caustic alkali solution, the saltsolution and water that are generated during this reaction form aspecifically heavier aqueous waste liquor that can be separated in asimple manner from the organic layer after the reaction.

The reaction temperature in the first stage amounts to approximately 80°C. with a reaction time of approximately 30 minutes. The reactiontemperature in the second stage amounts to 50° C. with a reaction timeof approximately 60 minutes.

The reaction of the hydroxyl-functional acrylate copolymer can also takeplace in a first sequential reaction. In this case, one is dealing witha phase-transfer catalyzed two-phase reaction between thehydroxyl-functional acrylate copolymer, the epihaloalkane and an aqueouscaustic alkali solution, preferably sodium hydroxide solution. Use ismade in this connection of quaternary ammonium compounds and/orphosphonium compounds as the phase-transfer catalysts. For example,benzyltrimethylammonium bromide, tetramethylammonium bromide,benzyltrimethylammonium chloride, ethyltriphenylphosphonium bromide andbutyltriphenylphosphonium chloride may be used; andbenzyltrimethylammonium bromide is preferred.

The temperature for the reaction stage amounts to 60° C. with a reactiontime of approximately 60 minutes. A variation of the phase transferprocess is the so-called azeotropic process in which the water that ispresent and that is formed during the two-phase reaction is distilledoff azeotropically under vacuum together with the epihaloalkane.

By way of example, the following may be designated as suitableepihaloalkanes: 1-chloro-2,3-epoxypropane (epichlorohydrin),1-chloro-2-methyl-2,3-epoxypropane and 1-chloro-2,3-epoxybutane.1-chloro-2,3-epoxypropane is preferred. Naturally, use can also be made,with success, of still further epihaloalkanes, e.g., epibromhydrin.

The acrylate copolymers (A), which contain epoxy groups, have a glasstransition temperature of 20° C. to 120° C. The preferred glasstransition temperature lies in the range from 30° C. to 90° C. Themolecular weights (Mw) generally amount to 1,000 to 30,000 or,preferably, 1,000 to 20,000. The epoxide number of theepoxide-containing acrylate copolymer in accordance with the inventionlies in the range from 0.018 to 0.510 or, especially, from 0.035 to0.412 equivalents/100 g!.

Aliphatic polybasic acids, preferably, dibasic acids such as, forexample, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacicacid, malonic aid, succinic acid, glutaric acid, 1,12-dodecanedioicacid, etc. can be used as the hardening agent--component (B). Theanhydrides of these acids can also be used, e.g., glutaric anhydride,succinic anhydride as well as the polyanhydrides of these dicarboxylicacids. These polyanhydrides are obtained via the intermolecularcondensation of the designated aliphatic dibasic dicarboxylic acids.Examples are the (poly)anhydride of adipic acid, the (poly)anhydride ofazelaic acid, the (poly)anhydride of sebacic acid, the (poly)anhydrideof dodecanedioic acid, etc. The polyanhydrides have a molecular weight(weight average, based on a polystyrene standard) of 1,000 to 5,000. Thepolyanhydrides can also be modified with a polyol.

The polyanhydrides can also be used as hardening agents when inadmixture with the aliphatic dibasic dicarboxylic acids or when inadmixture with hydroxycarboxylic acids that have melting points between40° C. and 150° C., e.g., 12-hydroxystearic acid, 2-hydroxyoctadecanoicacid, 3-hydroxyoctadecanoic acid or 10-hydroxyoctadecanoic acid, and2-hydroxymyristic acid.

Cycloaliphatic dicarboxylic acids such as, for example,1,4-cyclohexanedicarboxylic acid or their polyanhydrides can also beused as hardening agents.

Suitable hardening agents are also amorphous and semi-crystallinecopolyesters. Both the amorphous and the semi-crystalline copolyesterscan be prepared in conformity with the condensation processes that areknown for polyesters (esterification and/or trans-esterification) inaccordance with the prior art. Suitable catalysts such as, for example,dibutyltin oxide or titanium tetrabutylate can also be used if required.

Suitable amorphous carboxy-functional copolyester resins have an acidnumber of 10 to 200 mg KOH/g! and a glass transition temperature of >40°C. Amorphous carboxy-functional copolyesters mainly contain aromaticpolybasic carboxylic acids as the acid components such as, for example,terephthalic acid, isophthalic acid, phthalic acid, pyromellitic acid,trimellitic acid, 3,6-dichlorophthalic acid, tetrachlorophthalic acidand, if available, the anhydride s!, chloride s! or ester s! thereof.Usually, they contain at least 50 mole-% of terephthalic acid and/orisophthalic acid or, preferably, 80 mole-%. The remainder of the acids(the difference up to 100 mole-%) consists of aliphatic and/orcycloaliphatic polybasic acids such as, for example,1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid,hexahydroendomethyleneterephthalic acid, hexachlorophthalic acid,azelaic acid, sebacic acid, decanedicarboxylic acid, adipic acid,dodecanedicarboxylic acid, succinic acid, maleic acid or dimeric fattyacids, hydroxycarboxylic acids and/or lactones such as, for example,12-hydroxystearic acid, ε-caprolactone or neopentyl glycolhydroxypivalate can also be used. Use is also made, in small quantities,of monocarboxylic acids such as, for example, benzoic acid, tertiarybutylbenzoic acid, hexahydrobenzoic acid and saturated aliphaticmonocarboxylic acids.

As far as suitable alcohol components are concerned, one may designatethe aliphatic diols such as, for example, ethylene glycol,1,3-propanediol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, 2,2-dimethylpropane-1,3-diol (neopentyl glycol),2,5-hexanediol, 1,6-hexanediol, 2,2- bis-(4-hydroxycyclohexyl)!propane,1,4-dimethylolcyclohexane, diethylene glycol, dipropylene glycol and2,2-bis- 4-(2-hydroxy)!phenyl propane. Polyols are also used in smallquantities such as, for example, glycerol, hexanetriol, pentaerythritol,sorbitol, trimethylolethane, trimethylolpropane andtris(2-hydroxy)-isocyanurate. Epoxy compounds can also be used insteadof diols or polyols. The proportion of neopentyl glycol and/or propyleneglycol in the alcohol component preferably amounts to at least 50 mole-%based on the total acids.

Suitable semi-crystalline polyesters have an acid number of 10 to 400 mgKOH/g! and an accurately defined DSC melting point. Thesesemi-crystalline polyesters are the condensation products of aliphaticpolyols, preferably aliphatic diols, and aliphatic and/or cycloaliphaticand/or aromatic polybasic carboxylic acids, preferably dibasic acids. Byway of example, one may designate as the aliphatic polyols: ethyleneglycol (1,2-ethanediol), propylene glycol (1,3-propanediol), butyleneglycol (1,4-butanediol), 1,6-hexanediol, neopentyl glycol,cyclohexanedimethanol, trimethylolpropane, etc. Aliphatic diols such as,for example, ethylene glycol, butylene glycol or 1,6-hexanediol arepreferred.

Suitable polybasic carboxylic acids are aliphatic dicarboxylic acids or,preferably, C₄ -C₂₀ dicarboxylic acids such as, for example, adipicacid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, succinicacid, undecanedicarboxylic acid and the aromatic dicarboxylic acids suchas, for example, terephthalic acid, isophthalic acid, phthalic acid andtheir hydrogenation products such as, for example,1,4-cyclohexanedicarboxylic acid. Aliphatic dicarboxylic acids with 6 to12 carbon atoms are preferred. Naturally, use can also be made ofmixtures of various polyols and polybasic carboxylic acids. Suitablecarboxy-functional acrylate polymers have an acid number of 10 to 400 mgKOH/g!.

Mixtures of variously suitable hardeners can also be used in thethermosetting powder coating compositions.

Based on the acrylic resin, the quantity of the anhydrides and/or acidsthat is used as the hardening agent--component (B)--can vary over a widerange and is governed by the number of epoxide groups in the acrylateresin (A). In general, a molar ratio of carboxy groups or, as the casemay be, anhydride groups to epoxide groups of 0.4-1.4:1 is selected or,preferably, 0.8-1.2:1.

In the coating system according to the invention, such conventionalpigments and/or fillers and/or additives can be present as are commonlyused for the preparation and use of powder coatings. These includeadditives from the group of accelerators, flow-promoting agents anddegassing agents, heat stabilizers, UV stabilizers, and/or HALSstabilizers and/or tribo-additives as well as matting agents if requiredsuch as, for example, waxes.

The preparation of the powder coatings in accordance with the inventionpreferably takes place in the melt as a result of the communal extrusionof all the formulation components at temperatures between 60° C. and140° C. The extruded material is then cooled, ground and selectivelysieved to a grain size that is smaller than 90 μm. Alternatively, otherprocesses for the preparation of the powder coatings are also suitablesuch as, for example, mixing together the formulation components insolution, with subsequent precipitation or removal of the solvent bydistillation.

The application of the powder coatings in accordance with the inventionis carried out by any process commonly used for such purposes such as,for example, by means of electrostatic spraying devices (corona ortribo) or using a fluidized bed process.

Powder coatings prepared as described herein may be applied tosubstrates such as metal and baked for, e.g., 5-60 minutes at 160° C. to220° C. to form a hard thermoset protective finish which is thermallystable and resistant to solvents, and which has good metal adhesionproperties, good mechanical strength and high durability, e.g., againstweathering.

The preparation and the properties of thermosetting powder coatingcompositions in accordance with the invention are illustrated below bythe following examples.

Preparation of Hydroxyl-functional Acrylate Copolymers

EXAMPLES 1 AND 2

General procedure:

Part I (see Table 1) is introduced into a stainless steel reactorequipped with a stirring device, a cooling device and a heating devicetogether with electronic temperature control. Part I is heated undernitrogen up to the point of refluxing. Part II and Part III (seeTable 1) are then slowly added in parallel over a period of 3 hours,during the course of which the reaction mixture is boiled under reflux.After addition of Part II and Part III has been terminated, the reactionmixture is boiled for a further 2 hours under reflux. The solvent isthen removed from the reaction mixture under vacuum.

                  TABLE 1    ______________________________________    Acrylate Copolymers Containing Hydroxyl Groups    (weights are in g)                     Example 1                            Example 2    ______________________________________    Resin No.          I        II    Part I    xylene             1,000.00 1,000.00    Part II    ditertiary-butyl peroxide                       46.25    46.25    xylene             78.75    78.75    Part III    hydroxyethyl methacrylate                       537.43   429.89    n-butyl acrylate   185.00   185.00    methyl methacrylate                       780.70   888.23    styrene            809.38   809.38    mercaptopropionic acid                       57.90    57.90    ______________________________________

                  TABLE 2    ______________________________________    Properties of Resins I and II                    Example 1                           Example 2    ______________________________________    Resin No.         I        II    OH number  mg KOH/g!                      98.0     78.0    Tg  ° C.! (calculated)                      71       73    Molecular weight (Mw)                      7,900    7,800    ______________________________________

Preparation of Epoxide-containing Acrylate Copolymers of the Invention

EXAMPLE 3

560 g of resin No. I were dissolved in 2,000 g of toluene in a 20 literreactor that is capable of being heated and that has been equipped witha thermometer, a stirrer and a reflux column. After the addition of 18ml of boron trifluoride ethyl etherate, the temperature was increased to80° C. and 100 g of epichlorohydrin were added dropwise over a period ofone hour. After this, stirring was continued for 30 minutes at 80° C.and then the mixture was cooled to 50° C. After the addition of 200 g ofaqueous caustic soda (22%), the mixture was stirred for a further hourat 50° C. After this, the aqueous phase was separated. Resin No. III wasobtained (properties: see Table 3) after vacuum distillation of theorganic phase at a temperature of 130° C. under reduced pressure (1 mmHg).

EXAMPLE 4

560 g of resin No. I were dissolved in 2,000 g of toluene and 1,000 g ofepichlorohydrin at 60° C. in a 20 liter reactor that is capable of beingheated and that has been provided with a thermometer, a stirrer and areflux column. After the addition of 18.6 g of benzyltrimethylammoniumchloride, 200 g of aqueous caustic soda (22%) were added and the mixturestirred for one hour at 60° C. After this, the aqueous phase wasseparated. Resin No. IV was obtained (properties: see Table 3) aftervacuum distillation of the organic phase at a temperature of 130° C.under reduced pressure (1 mm Hg).

EXAMPLE 5

700 g of resin No. II were dissolved in 2,000 g of toluene in a 20 literreactor that is capable of being heated and that has been provided witha thermometer, a stirrer and a reflux column. After the addition of 18ml of boron trifluoride ethyl etherate, the temperature was increased to80° C. and 100 g of epichlorohydrin were added dropwise over a period ofone hour. After this, it stirring was continued for 30 minutes at 80° C.and then the mixture was cooled to 50° C. After the addition of 200 g ofaqueous caustic soda (22%), the mixture was stirred for a further hourat 50° C. After this, the aqueous phase was separated. Resin No. V wasobtained (properties: see Table 3) after vacuum distillation of theorganic phase at a temperature of 130° C. under reduced pressure (1 mmHg).

EXAMPLE 6

700 g of resin No. II were dissolved in 2,000 g of toluene and 1,000 gof epichlorohydrin at 60° C. in a 20 liter reactor that is capable ofbeing heated and that has been provided with a thermometer, a stirrerand a reflux column. After the addition of 18.6 g ofbenzyltrimethylammonium chloride, 200 g of aqueous caustic soda (22%)were added and the mixture stirred for one hour at 60° C. After this,the aqueous phase was separated. Resin No. VI was obtained (properties:see Table 3) after vacuum distillation of the organic phase at atemperature of 130° C. under reduced pressure (1 mm Hg).

                  TABLE 3    ______________________________________    Properties of Resins III to VI           Example 3                   Example 4 Example 5 Example 6    ______________________________________    Resin No.             III       IV        V       VI    Initial resin             I         I         II      II    E Number 0.145     0.146     0.117   0.118     equiv./100 g!    Tg  ° C.!             69        70        70      71    (calculated)    Molecular             7,900     7,900     7,800   7,800    weight (Mw)    ______________________________________

Preparation of Powder Coatings

EXAMPLES 7 and 8

840 parts by weight of Resin III (example 7) or Resin IV (example 8),150 parts by weight of dodecanedicarboxylic acid, 5 parts by weight ofResiflow® PV 88 and 5 parts by weight of benzoin were mixed for 30seconds in the dry state in a Henschel mixer at 700 RPM and thenextruded in a Buss-Co-Kneader (PLK 46) extruder using a jackettemperature of 100° C., a cooled screw conveyor and a rate of rotationof the screw of 150 RPM. The extruded material was cooled, ground andselectively sieved to less than 90 μm.

The powder coatings were applied electrostatically to aluminum sheets (Qpanel AL-36 5005 H 14/08 (0.8 mm)) and cured at a temperature of 200° C.using a curing time of 15 minutes.

Table 4 shows the technical properties of the resultant lacquers.

EXAMPLES 9 and 10

870 parts by weight of Resin V (example 9)or Resin VI (example 10), 120parts by weight of dodecanedicarboxylic acid, 5 parts by weight ofResiflow® PV 88 and 5 parts by weight of benzoin were mixed for 30seconds in the dry state in a Henschel mixer at 700 RPM and thenextruded in a Buss-Co-Kneader (PLK 46) extruder using a jackettemperature of 10020 C., a cooled screw conveyor and a rate of rotationof the screw of 150 RPM. The extruded material was cooled, ground andselectively sieved to less than 90 μm.

The powder coatings were applied electrostatically to aluminum sheets (Qpanel AL-36 5005 H 14/08 (0.8 mm)) and cured at a temperature of 200° C.using a curing time of 15 minutes.

Table 4 shows the technical properties of the resultant lacquers.

                  TABLE 4    ______________________________________              Example 7                     Example 8                              Example 9                                       Example 10    ______________________________________    Resin basis III      IV       V      VI    Gelation time                30       31       27     28    Kofler rack    200° C.    Gloss       109      108      108    109    (60° DIN 67530)    Flow properties                very good                         very good                                  very good                                         very good    Erichsen penetration                9.9      9.8      9.8    9.9    (DIN 53156) (mm)    Cross cut   0        0        0      0    (DIN 52151)    Impact      30       40       30     20    (ASTM D 2794,    back side)    ______________________________________

We claim:
 1. A process for the preparation of a glycidylether-containing acrylate copolymer, comprising:preparing ahydroxyalkyl-functional (meth)acrylate copolymer and then reacting itwith an epihalohydrin to provide an (meth)acrylate copolymer containingglycidyl ether groups.
 2. A process in accordance with claim 1, whereinsaid hydroxy-functional acrylate copolymers are prepared in aradical-initiated copolymerization of a monomer mixture comprising:(a) 0to 70 parts by weight of methyl (meth)acrylate; (b) 0 to 60 parts byweight of C₂ -C₁₈ alkyl or cycloalkyl esters of acrylic acid; (c) 0 to90 parts by weight of vinyl aromatic compounds; (d) 1 to 95 parts byweight of hydroxyl esters of acrylic acid and/or methacrylicacid,wherein the sum of the parts by weight of components (a) through(d) results in
 100. 3. A process in accordance with claim 2, wherein thecopolymerization process is carried out at temperatures from 60 to 160°C. in the presence of a radical initiator and, optionally, a molecularweight regulator.
 4. A process in accordance with claim 2, wherein theradical-type copolymerization is carried out by solution polymerizationor bulk polymerization.
 5. A process in accordance with claim 4, whereinthe solution copolymerization is carried but in an inert solventselected from the group consisting of benzene, toluene, xylene, ethylacetate, butyl acetate, hexyl acetate, heptyl acetate, methylglycolacetate, ethylglycol acetate, tetrahydrofuran, dioxane, diethyleneglycol dimethyl ether, acetone, methyl ethyl ketone, methyl isobutylketone, methyl n-amyl ketone, methyl isoamyl ketone and mixturesthereof.
 6. A process in accordance with claim 2, wherein thecopolymerization is carried out continuously via uniform metering of themonomer mixture and radical initiator into a reaction vessel andcontinuously draining off of the resultant copolymer.
 7. A process inaccordance with claim 2, wherein the copolymerization is carried outdiscontinuously, with a constant addition of the monomer mixture into astirred vessel and without recovery of copolymer until the reaction isterminated.
 8. A process in accordance with claim 2, wherein thepolymerization is carried out at atmospheric pressure or at pressures ofup to 25 bars.
 9. A process in accordance with claim 2, wherein weightregulators are added to the copolymerization mixture in quantities of0.1% to 10% by weight based on the total weight of the monomers.
 10. Aprocess in accordance with claim 1, wherein the epihalohydrin isselected from the group consisting of: 1-chloro-2,3-epoxypropane,1-chloro-2-methyl-2,3-epoxypropane, 1-chloro-2,3-epoxybutane, andepibromohydrin.
 11. A process in accordance with claim 1, wherein thereaction is catalyzed using quaternary phosphonium or ammonium compoundsselected from the group consisting of benzyltrimethylammonium bromide,tetramethylammonium bromide, benzyltrimethylammonium chloride,ethyltriphenylphosphonium bromide, butyltriphenylphosphonium chloride,and mixtures thereof.
 12. A method for making a glycidylether-containing (meth)acrylate copolymer, comprising the stepsof:preparing a solution of a hydroxyalkyl-functional (meth)acrylatecopolymer in an inert solvent; adding a Lewis acid catalyst and anexcess of epihalohydrin to said solution and permitting an additionreaction to proceed until an addition product is obtained; andthereafter, adding an aqueous alkali solution to the addition productand permitting a dehydrohalogenation reaction to proceed until formationof a glycidyl ether-containing (meth)acrylate copolymer is substantiallycomplete.
 13. A method as defined in claim 12, wherein said inertsolvent is benzene, toluene or chloroform.
 14. A method as defined inclaim 12, wherein said Lewis acid catalyst comprises boron trifluoride,boron trifluoride ethyl etherate or tin tetrachloride.
 15. A method asdefined in claim 12, wherein the aqueous alkali solution comprisesaqueous sodium hydroxide solution.
 16. A method as defined in claim 12,wherein said addition reaction is permitted to proceed at a temperatureof about 80° C. for a period of about 30 minutes.
 17. A method asdefined in claim 12, wherein said dehydrohalogenation reaction ispermitted to proceed at a temperature of about 50° C. for a period ofabout 60 minutes.
 18. A method for making a glycidyl ether-containing(meth)acrylate copolymer, comprising the steps of:providing anepihalohydrin solvent; adding a Lewis acid catalyst and ahydroxyalkyl-functional (meth)acrylate copolymer to the epihalohydrinsolvent and permitting an addition reaction to proceed until an additionproduct is obtained; and thereafter, adding an aqueous alkali solutionto the addition product and permitting a dehydrohalogenation reaction toproceed until formation of a glycidyl ether-containing (meth)acrylatecopolymer is substantially complete.
 19. A method as defined in claim18, wherein said Lewis acid catalyst comprises boron trifluoride or tintetrachloride.
 20. A method as defined in claim 18, wherein the aqueousalkali solution comprises aqueous sodium hydroxide.
 21. A method asdefined in claim 18, wherein said addition reaction is permitted toproceed at a temperature of about 80° C. for a period of about 30minutes.
 22. A method as defined in claim 18, wherein saiddehydrohalogenation reaction is permitted to proceed at a temperature ofabout 50° C. for a period of about 60 minutes.
 23. A method for making aglycidyl ether-containing (meth)acrylate copolymer, comprising the stepsof:dissolving a, hydroxyalkyl-functional (meth)acrylate copolymer in aninert solvent; adding an excess amount of epihalohydrin; adding a phasetransfer catalyst; adding aqueous caustic soda; and thereafter, stirringthe two-phase phase transfer reaction mixture at a temperature of about60° C. until formation of a glycidyl ether-containing (meth)acrylatecopolymer is substantially complete.
 24. A method as defined in claim23, wherein said inert solvent is benzene, toluene or chloroform.
 25. Amethod as defined in claim 23, wherein said phase transfer catalyst isselected from the group consisting of: quaternary ammonium compounds andquaternary phosphonium compounds.